1. Field of the Invention
This invention relates generally to the formation of a solid article from a mathematical or graphical representation and more particularly to a system for generating the shape of an article by actinic irradiation of successive sheets which comprise a matrix which supports the article during formation.
2. Related History
Since the implementation of computer technology for physical design purposes, there has been an appreciation of the need for expanding use of computers to control the fabrication of prototypes of articles which have been designed. While the principle of irradiating an article to effect changes in molecular structure and physical properties has been long recognized, such phenomenon had not been employed for the purpose of generating three-dimensional articles until recent years. In this regard, attempts have been made to utilize a fluid medium containing a curable material which was irradiated by a plurality of beams. The energy level at the intersection of the beams was sufficient to cure the material within the fluid medium. Such apparatus did not gain widespread acceptance due to many inherent disadvantages including cost, resolution difficulties and insufficient energy levels as a result of absorption as the depth of beam penetration into the fluid medium increased.
In U.S. Pat. No. 4,575,330, an apparatus for constructing an article by ultra violet polymerization of the upper surface of a photopolymeric fluid medium was disclosed. Successive layers of the article were generated by successively lowering built up polymerized layers into the fluid medium so that the upper surface of the fluid medium contained unpolymerized material suitable for polymerization and generation of the next layer.
While the apparatus did not require multiple beams, it suffered from several disadvantages, including restricted photopolymeric material requirements. It was limited to use with ultra violet beams and required photopolymers responsive to the ultra violet wavelengths. In addition, difficulties were encountered in maintaining the upper surface of the fluid medium at a planar reference level due to fluid turbulence, reduction in fluid level as a result of the polymerization of prior layers and uneven shrinkage of the polymerized material. Also, the apparatus lacked precise control over the depth of polymerization into the fluid medium which resulted in loss of axial resolution.
Further, because a fluid medium was used, the article being constructed could not be supported except by the underlying built up article layers and a support platform, movable within the medium, was required. As such, articles having surfaces contoured with undercuts and the like could not be generated without providing a complicated mechanism capable of moving the platform along multiple axes.
In addition, in order to provide sufficient energy levels for curing, the maximum scan speed of the ultra violet beam was relatively slow, resulting in a correspondingly slow overall throughput.
In copending application Ser. No. 07/312,613 filed Feb. 17, 1989, an article shaping system was described wherein sheets of thermoplastic polymer mixture were stacked on a platen and the uppermost sheet was irradiated with an electron beam deflected to trace the configuration of a incremental planar heighth of the article. The beam effected cross-linking of the polymer along the trace to convert, for example, a thermoplastic polymer to a thermoset. As successive sheets were placed on top of one another and irradiated, the stack formed a matrix which supported the built up configuration of the article. The matrix was thereafter removed by heat and/or solvents. Such system provided enhanced image resolution, reduced mechanical complexity and greater material compatibility than prior methods. Throughput was increased because the electron beam provided an efficient irradiation source and the sheets could be stacked and referenced rapidly.
Unfortunately, the production of large and detailed components could still take many hours. Further, the efficient production of a suitable electron beam required expensive evacuation hardware systems and high voltage biasing equipment. Additionally, image penetration into underlying sheets presented a problem which could be alleviated by precise control of the beam energy level or the use of sheets of polymer mixture with depthwise varying degrees of reactivity.
A system for computer aided generation of three dimensional articles utilizes sheets of thermoplastic polymer mixture adhered in discrete locations on a continuous carrier web. Successive sheets are individually imaged with actinic radiation in the configuration of successive incremental planar heighths of the article. The actinic radiation affects the tendency of the imaged areas of each sheet to undergo subsequent curing which results in a modification of a physical property such as a change in solubility and/or rheology. The irradiated sheets are stripped from the carrier web and stacked in a matrix. The imaged areas of all sheets are simultaneously cured with heat and/or aging.
Depending upon the particular polymer mixtures employed, the actinic radiation serves, e.g. to facilitate subsequent curing which changes a thermoplastic into a thermoset or alters the solubility of a constituent polymer in a particular solvent by modifying functional side groups of linearly branched polymer chain structures and/or the molecular weight of the polymer.
The polymer mixture chosen for the sheets comprises a base resin, a reactive diluent and a reaction modifying compound coupled with an activating compound responsive to the radiation employed for imaging. Although the components of the polymer mixture are functionally distinct, they are not required to be physically distinct.
For catalytically induced reactions, the base resins are typically higher molecular weight polymers which act as film formers and contain functional groups typical of such reactions, e.g. epoxy, hydroxy, carboxy. The reactive diluents contain mono- or multi-functionalities typically co-reactive with those of the base resin, and are generally lower molecular weight monomers, oligomers, or prepolymers which, when reacted with the base resin, substantially alter the physical and/or chemical properties of the polymer mixture. Reaction modifying compounds include cationic photo catalysts such as diaryliodonium, triarylsulfonium, and mixed-ligand arene cyclopentadienyl metal salts, and may also include photosensitizers compatible with such catalysts.
In lieu of catalytic activation mechanisms, an article shape can be realized through a photo-activated deprotection of reactive functionalities which results in subsequent polymer structure modification. The base resins employed are film forming polymers which may contain blocked and/or mutually non-reactive free functionalities such as suitable combinations of hydroxyl, aldehyde, amine, and isocyanate moieties. The reactive diluents contain mono- or multi-functionalities which may be co-reactive with those of the base resin. The diluents are generally lower molecular weight monomers, oligomers and prepolymers with blocked and/or mutually non-reactive free functionalities.
The reaction modifying protecting groups are previously reacted with specific functionalities in either the base resin or the reactive diluent or both, and cleave under actinic radiation to free these functionalities. Cleavage may be obtained by a direct photolytic activation, or indirectly such as by a photo-catalyzed de-blocking. Additional photo-sensitizing compounds may be used to alter the spectral-response of these reactions.
The sheets of polymer mixture are adhered onto the carrier web in discrete areas and comprise a substantially uniform thickness stratum of polymer mixture. When the stratum is not typically self-adherent, a substratum or tack layer may be formed of a polymer mixture similar to the stratum with lower molecular weight constituents or additional tackifying resins to temporarily adhere the sheet to the web and to thereafter adhere imaged sheets to one another when stacked.
An apparatus for imaging and consolidating the sheets includes a mechanism for transporting successive sheets carried on the web to an imaging station and for transporting the imaged sheets to a stacking station. The imaging station includes a cathode ray tube or a sequence of photomasks, and an optical projection system. At the stacking station the sheets are stripped from the web and placed on a stack which forms a matrix.
The image irradiated on each sheet comprises the configuration of the article to be formed at an incremental heighth which conforms to the thickness and Dosition of such sheet. The actinic radiation initiates a modification of the reactive properties of the imaged areas on a sheet. Under the subsequent influence of heat and/or age curing, a substantially simultaneous differentiation of the image and non-image areas of the sheets occurs. After curing, the remainder of the stack is removed by heat, pressure or chemical dissolution or dispersion.
From the foregoing compendium, it will be appreciated that it is an aspect of the present invention to provide an article shaping system of the general character described which is not subject to the disadvantages of the related history aforementioned.
A feature of the present invention is to provide an article shaping system of the general character described capable of constructing three-dimensional prototypes of computer designed articles with precise dimensional accuracy.
A consideration of the present invention is to provide an article shaping system of the general character described which does not require complex mechanical structures or multiple irradiation beams to form intricate shapes.
It is another consideration of the present invention to provide an article shaping system of the general character described wherein the article may be formed from a wide variety of materials having different physical properties.
Another feature of the present invention is to provide an article shaping system of the general character described capable of generating a three-dimensional article with relatively high speed.
To provide an article shaping system of the general character described which is relatively low in cost is a further aspect of the present invention.
Providing a computer controlled article shaping system of the general character described with enhanced vertical definition is another aspect of the present invention.
A further consideration of the present invention is to provide an article shaping system of the general character described which utilizes low intensity actinic rays for configuring an article shape in successive sheets of a built up support matrix.
Another feature of the present invention is to provide an article shaping system of the general character described which utilizes actinic imaging for initiating latent chemical modification in the form of the shape of an incremental planar heighth of an article on successive sheets of a support matrix.
A still further feature of the present invention is to provide a method of the general character described for shaping an article whereby the configuration of the article is generated by latent imaging of sheets which are stacked to provide a support matrix for the article as its shape is being generated.
Yet another aspect of the present invention is to provide an article shaping system of the general character described which is relatively simple to use.
Other aspects, features and considerations in part will be obvious and in part will be pointed out hereinafter.
With these aims in view, the invention finds embodiment in certain combinations of elements, arrangements of parts and series of steps by which the said aspects, features and considerations and certain other aspects, features and considerations are attained, all with reference to the accompanying drawings and the scope of which is more Darticularly pointed out and indicated in the appended claims.